Impacts of the Diurnal Radiation Cycle on the Formation, Intensity and Structure of Hurricane Edouard (2014)

This work examines the impacts of the diurnally varying radiation cycle on the formation, intensity, structure, and track of Hurricane Edouard (2014) at different stages of its lifecycle through convection-permitting simulations. During the formation stage, nighttime destabilization through radiative cooling may promote deep moist convection that eventually leads to the genesis of the storm, while a tropical cyclone fails to develop in the absence of the night phase despite a strong incipient vortex under moderately strong vertical wind shear. The nighttime radiative cooling further enhances the primary vortex before the storm undergoes rapid intensification (RI). Thereafter, the nighttime radiative cooling mainly increases convective activities outside of the primary eyewall that lead to stronger/broader outer rainbands and larger storm size during the mature stage of the hurricane;there is, however, little impact on the hurricane's intensity in terms of maximum 10-m surface wind speed. The control forecast undergoes distinct secondary eyewall formation during the mature stage of Edouard (as observed), while there is no apparent eyewall replacement cycle (ERC) as simulated in sensitivity experiments without solar insolation (nighttime only)and the moat is narrower in those with switch-on solar insolation at night (daytime only), suggesting the potential role of the diurnally varying radiative impact. Through changing the strength of the initial vortex during the formation stage, the diurnal cycle may also alter the track of the storm.